The invention relates to diesel fuel compositions containing oxygenated compounds derived from tetrahydrofurfuryl. It also relates to new oxygenated compounds derived from tetrahydrofurfuryl.
Today, the improvement of air quality is an absolute priority in all the large industrialized countries. Among the referenced emitters of pollutants, transport occupies a place that requires considerable measures to be taken to reduce its contribution. It is because of this that successive regulatory measures appeared several years ago, with new restrictions from the year 2000, in particular specifications on fuel quality. In fact, besides the characteristics conventionally specified, new regulations on the chemical composition of fuels have appeared, with the aim of limiting the precursors of some pollutants, such as particles, and compounds which react with tropospheric ozone or toxic compounds. In this context, it is obvious that all attempts aiming to improve the quality of products in order to offer mixtures that significantly reduce polluting emissions are promising.
It is one of the objects of the invention to propose the use of oxygenated compounds derived from tetrahydrofurfuryl as additives or formulation bases of gas-oils and leading to a significant lowering of particle emissions.
The oxygenated compounds used in the diesel fuels according to the invention have the general formula: 
in which xe2x80x94Xxe2x80x94 is chosen from:
xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94[CH2xe2x80x94O]nxe2x80x94 with n comprised of between 1 and 20
and xe2x80x94R is chosen from:
the alkyl groups containing from 1 to 30 carbon atoms, amongst which for example are the isopropyl, isobutyl, tertbutyl and tertamyl groups; and
the groups containing a tetrahydrofurfuryl unit, for example 
Among the preferred compounds for use in the diesel fuel compositions according to the invention, the following can be mentioned:
tetrahydrofurfuryl tertbutyl ether (I); and
acetal or a ditetrahydrofurfuryl polyacetal (II).
Their respective formulae are given below: 
with n comprised between 1 and 20.
The different synthesis routes for these preferred compounds are described below.
Tetrahydrofurfuryl tertbutyl ether (I) can be prepared for example:
by reacting tetrahydrofurfuryl alcohol with for example a tertbutyl halide according to a standard esterification process, for example using Williamson""s reaction; or
by adding tetrahydrofurfuryl alcohol to isobutene preferably using an acid catalyst chosen for example from sulfuric acid, sulphonic alkylbenzene acids and sulphonated polystyrene resins, such as Amberlyst 15(copyright) resin. It is the synthesis method that will be described in more detail in Example 1.
Ditetrahydrofurfuryl acetal and polyacetals (II) are generally produced from the reaction of tetrahydrofurfuryl alcohol with formaldehyde, either in its monomer form, or in its polymer form called paraformaldehyde of (CH2O)x structure, or in its cyclic trimer form called trioxane, of formula: 
It is this latter synthesis route which is illustrated in Example 2.
This reaction is in general catalyzed by acids such as for example sulfuric acid, sulphonic resins such as Amberlyst 15(copyright) resin or the Lewis acids.
These products can also be prepared by exchange reaction between tetrahydrofurfuryl acid and an acetal such as for example dimethoxymethane, also called methylal.
In the fuel compositions for diesel engines according to the invention, the oxygenated compounds derived from tetrahydrofurfruyl can be used in low concentrations, as additives, in standard diesel fuels of petroleum origin (middle distillates of petroleum), optionally containing in varying proportions, other oxygenated compounds such as alkyl esters derived from vegetable oils. They can also be used as additives. The concentration of oxygenated compounds according to the invention can thus be for example from 0.01 to 1%, preferably from 0.05 to 0.2% by weight.
The oxygenated compounds derived from tetrahydrofurfuryl can also be used as basic constituents of diesel fuel. In this use, they can represent for example up to 40% and preferably up to 30% by weight of the fuel.
More usual proportions of oxygenated compounds derived from tetrahydrofurfuryl are in the region of 10 to 15% by weight.
In all of the cases mentioned above the fuels for diesel engines according to the invention can still contain all the other conventional additives, in the usual concentrations.
According to the invention, the fuels described above can supply all types of diesel engines, with direct or indirect fuel injection.
The invention also provides new oxygenated compounds of tetrahydrofurfuryl, namely ditetrahydrofurfuryl polyacetals of formula (II) with n greater than 1.
The following examples illustrate the invention without limiting it.